Substances and compounds containing fibers of different characteristics are of special interest. For disintegrating such materials and compounds numerous devices are known such as crushers, granulators, defibrators and so on. Apart from knife ring flakers in the first instance, wing beater mills, hammer mills, shredders and derivations thereof must be mentioned.
Wing beater mills, cross stream mills and double stream mills have as a main characteristic a rotor and, as a functional counterpart, a screen or friction ring or a combination of both encircling the rotor as a whole. The raw material to be disintegrated is fed axially to the rotor and centrifugally accelerated by the rotor blades towards the surrounding screen or friction ring. Wear plates fixed to the ends of the rotor blades drag the material to be milled along the surrounding screen oror friction ring, until it is disintegrated to an extent that it is able to pass through the screen perforations. The screen perforations are the bottle neck of the system. The smaller they are, the more often the material has to be dragged by the rotor along the surrounding screen or friction ring, until it is sufficiently disintegrated to be able to pass through the perforations. The smaller the perforation, the more times the material to be ground has to be dragged along the screen ring, until it is sufficiently disintegrated and can finally pass through the screen holes. The output drops correspondingly and the energy consumption increases. If friction rings are employed instead of screen rings, the sufficiently disintegrated material has to leave the milling zone via the lateral slots between the rotor blades and the friction ring. They are bottle necks, too. Their negative effects are the more serious, the more finely that the material is to be disintegrated and the higher its moisture content.
With very moist or even sticky materials, the machines mentioned above fail entirely since the screen holes or lateral slots get plugged and the function of the machines breaks down. As a result, these machines are generally only used for disintegrating materials having a moisture content between 1 and 5 %, referred to dry matter, for example as chip disintegrators in particleboard manufacture. But dry wood flakes with 1 to 5% moisture content, are extraordinary brittle. When being disintegrated to fine flakes or even micro flakes, as required for good surface layers in particleboard manufacture, they do not break as desired in the longitudinal sense parallel to the main axis, but because of their high brittleness they break several times in an unfavourable manner transversely, resulting in a poor ratio of slenderness (length:cross-section). A poor ratio of slenderness again results in poor values for bending strength and poor homogeneity of the board surface. In contrast, moist wood is flexible and tough. It breaks preferably at points of natural weakness, for example in the vascular vessels or in the soft spring wood. The number of undesired transversal ruptures drops sizeably. A flake of favourable dimensions and high ratio of slenderness, i.e. a long and thin flake, emerges, as required for boards of high bending strength and good surface quality.
It is the aim of the invention to separate materials as well as waste materials consisting of at least two or more physically sufficiently different components into their individual components. It is also an aim to disintegrate structures as for example pulp fibers in a paper sheet to their original components, which means into pulp fibers. It is also an aim to execute such disintegration as carefully as possible in order to preserve the original sizes of particles, length of fiber and so on, in order to be able to repeat recycling operations as often as possible. An additional aim is to execute such disintegrating operations in all ranges of moisture and even in fluid suspensions or with sticky materials or when adding sticky additives. Furthermore, heat development shall be kept as low as possible in order to avoid evaporation of volatile materials.
The basic idea of the invention consists in a combination of several measures. In contrast to all machines according the state of the art, the tool ring according invention has a distinctly xe2x80x9copen circumferencexe2x80x9d. This has to be understood as the ratio of gaps between the tools referred to the total circumference of the tool ring. This is the basic precondition for avoiding plugging even with moist and sticky materials.
The total of all gaps between the tools is 4.100 mm. The total circumference is 5.100 mm. Then the xe2x80x9copen circumferencexe2x80x9d is 80,4 %. That means that 80,4% of the circumference is entirely open, so that material can pass through without any hindrance.
Machines corresponding to the state of the art have an xe2x80x9copen circumferencexe2x80x9d of only 25 to 45%.
Another important feature of machines according to the invention is the xe2x80x9clarge clear spanxe2x80x9d between one tool to the next being 15 to 25 times larger than with any comparable machine of the state of the art. Screen perforations with machines according the state of the art range between 1,5 to 3,0 mm for so-called xe2x80x9cConidur screensxe2x80x9d. xe2x80x9cSlot screensxe2x80x9d, as employed for example for producing micro flake surfaces in particleboard manufacture have slots in the range of 1,5xc3x9715 mm to 3,0xc3x9730,0 mm. In contrast, the free spaces of the machine according to the invention range between 40xc3x97400 mm to 55xc3x97500 mm, depending on the size of machine. That means that the size of particles of material fed into machines according the state of the art is a multiple of the size of screen perforations and therefore the material has to stay on the screen until it is entirely disintegrated. Even the disintegrated material is still larger than the screen perforations, so that the danger of plugging remains persistent, especially with moist material.
The situation is entirely different with the machine according to the invention: Here the free span from tool to tool is in general larger than the lengths of the input material. At a free span between the tools of for example 40 to 50 mm, no piece of the input is able to set and rest on the tools. Even with material of greater length such risk does not exist, as the high centrifugal force effects that long pieces sag and are flung through the gap between the tools. Last but not least, the machine according to the invention is constructed with shearing knives fixed to the rotor with the objective to shear off any build up of material on the tools greater then about 2 mm.
The principle of operation of the machine according the state of the art as well as the one according the invention is based on the radial acceleration of the input material. The tools according to the invention are rotated with a relative speed preferably between 30 and 100 m/sec around the rotor. The working edges (3.5) of the tools (3.3 . . . 3.6) intercept the radially accelerated material in flight more or less at a right angle and effect that the material bends around the working edges. Thereby, in each piece of input material, impulse-like bending and shearing strain are produced, which effects that the material is disintegrated at its weakest point or layer. Such weak points are for example spring wood, vascular vessels and parenchymatic tissue of the wood as well as natural tension and drying fissures, but also jointing points of elements of the same material, like particles in particleboard.
Machines of the state of the art are fixed by the supplier to a certain rotation speed in accordance with trials executed to determinate the optimal speed before delivery. Normally such speed is not subsequently changed. The determining parameters for the degree of disintegration are in the first instance the size of the screen perforations, the distance between the wear plates of the rotor and the screen or friction ring, the profile of the friction ring and its orientation. The output of the machine is a function of the selected screen or friction ring without a further possibility of adjustment or control.
The machine according invention is entirely different in design, control and possibilities of adjustment: Here the main adjusting parameters are the circumferential speeds of rotor (2) and tool ring (3) or of the working edge (3.5) of the tools (3.4 . . . 3.6). That""s why the motors of both rotor (2) and tool ring (3) are normally equipped with frequency converters enabling to adjust the speed continuously.
High speed effects a high degree of disintegration and a high output. Low speed means a low degree of disintegration and lower output.
Further means of control are modulating the speed of the rotor (2) or the speed of the tool ring (3) independently from each other. In general rotor (2) and tool ring (3) are rotated in opposite directions. But for certain applications rotating in the same direction at different speeds can yield favorable effects.
Another control parameter of the machine according invention is the quantity and speed of air passing through the machine. Both rotor (2) and tool ring (3) act as radial fans and generate about 3 to 6 times as much air as machines according to the state of the art. The reason for this is the large xe2x80x9copen circumferencexe2x80x9d of the tool ring (3), which does not throttle the air generated by the rotor (2).
Huge quantities of air passing through the machine at high speed result in scavenging the machine of disintegrated material within fractions of a second.
A special throttling device (6) at the inlet of the machine serves to adjust the quantity of air entering the machine over a continuous range. The throttle consists of at least one pull in belt (6.1) and a cross section adjustment plate (6.2), which can be replaced by a second pull in belt. This does not only limit the intake of air, but also reduces the speed of air and consequently the dwell time of the material in the machine. That again determines the throughput.
Another control parameter is the height of the tool (3.4) in the tool ring (3). There is a minimum of tools (3.6) of about xc2xc to ⅙ that must have a large height in order to guaranty a high transversal stiffness of the tool ring (3). They must be welded to the ring (3). The rest of the tools (3.4) are executed as interchangeable ones. Their height is selected in accordance with the technical requirements of the individual application. Tools (3.4) with a large height act like blower blades. The more of them that are installed in the tool ring (3), the greater the generation of air and the air velocity. If less air shall be generated, interchangeable tools (3.4) of low height must be installed.